1. Field of the Invention
The present invention relates to a thin film magnetic head for writing and a method of manufacturing the same, and more particularly relates to a combination type thin film magnetic head including an inductive type thin film magnetic head for writing and a magnetoresistive type magnetic head for reading, said magnetic heads being supported by a substrate in a stacked fashion.
2. Description of the Related Art
Recently a surface recording density of a hard disc device has been improved, and it has been required to develop a thin film magnetic head having an improved performance accordingly.
There has been proposed and actually used a combination type thin film magnetic head including an inductive type thin film magnetic head for writing and a magnetoresistive type magnetic head for reading, said magnetic heads being supported by a substrate in a stacked fashion. As the reading magnetic head utilizing the magnetoresistive effect, there has been generally used a reading magnetic head utilizing an anisotropic magnetoresistive (AMR) effect, but there has been also developed a magnetic head utilizing a giant magnetoresistive (GMR) effect having a resistance change ratio higher than the normal anisotropic magnetoresistive effect by several times.
In the present specification, these AMR and GMR elements are termed as a magnetoresistive type thin film magnetic head or simply MR reproducing element.
By using the AMR reproducing element, a very high surface recording density of several gigabits per a unit square inch has been realized, and a surface recording density can be further increased by using the GMR element. By increasing a surface recording density in this manner, it is possible to realize a hard disc device which has a very large storage capacity of more than 10 gigabytes and is still small in size.
A height (MR Height: MRH) of a magnetoresistive reproducing element is one of factors which determine a performance of a reproducing head including a magnetoresistive reproducing element. This MR height MRH is a distance measured from an air bearing surface on which one edge of the magnetoresistive reproducing element is exposed to the other edge of the element remote from the air bearing surface. During a manufacturing process of the magnetic head, a desired MR height MRH is obtained by controlling an amount of polishing the air bearing surface.
At the same time, a performance of a recording head has been also required to be improved. In order to increase a surface recording density, it is necessary to make a track density on a magnetic record medium as high as possible. For this purpose, a width of a pole portion at the air bearing surface has to be reduced to a value within a range from several micron meters to several sub-micron meters. In order to satisfy such a requirement, the semiconductor manufacturing process has been adopted for manufacturing the thin film magnetic head.
One of factors determining a performance of an inductive type thin film magnetic film for writing is a throat height (TH). This throat height TH is a distance of a pole portion measured from the air bearing surface to an edge of an insulating layer which serves to separate electrically a thin film coil from the air bearing surface. It has been required to shorten this distance as small as possible. Also this throat height TH is determined by an amount of polishing the air bearing surface.
In order to improve the performance of the combination type thin film magnetic head including a stack of an inductive type thin film magnetic head for writing and a magnetoresistive type thin film magnetic head for reading, it is important that the inductive type thin film magnetic head for writing and magnetoresistive type thin film magnetic head for reading are formed with a good balance.
FIGS. 1-11 show successive steps of manufacturing a known typical thin film magnetic head, in which A represents a cross sectional view cut along a plane perpendicular to the air bearing surface and B denotes a cross sectional view cut along a plane parallel with the air bearing surface. FIGS. 12-14 are a cross sectional view illustrating a completed thin film magnetic head, a cross sectional view of the pole portion, and a plan view depicting the whole magnetic head. This magnetic head belongs to a combination type thin film magnetic head which is constructed by stacking an inductive type thin film writing magnetic head and a magnetoresistive type thin film reading magnetic head one on the other.
At first, as illustrated in FIG. 1, on a substrate 1 made of, for instance aluminum-titan-carbon (AlTiC), is deposited an insulating layer 2 made of alumina (Al.sub.2 O.sub.3) and having a thickness of about 5-10 .mu.m.
Then, as depicted in FIG. 2, a first magnetic layer 3 constituting one of magnetic shields for protecting the MR reproducing magnetic head from external magnetic fields is formed to have a thickness of 3 .mu.m on the insulating layer.
Then, after depositing by sputtering a shield gap layer 4 made of an alumina with a thickness of 100-150 nm as shown in FIG. 3, a magnetoresistive layer 5 having a thickness of several tens nano meters and being made of a material having the magnetoresistive effect, and the magnetoresistive layer is shaped into a desired pattern by a highly precise mask alignment.
Next, as represented in FIG. 4, a second shield gap layer 6 made of an alumina is formed to embed the magnetoresistive layer 5 within the shield gap layers 4, 6.
Next, as shown in FIG. 5, a second magnetic layer 7 made of a permalloy and having a thickness of 3 .mu.m is formed. This magnetic layer 7 serves not only as the other shield layer (top shield) for magnetically shielding the MR reproducing element together with the above mentioned first magnetic layer 3, but also as one of poles (bottom pole) of the inductive type writing thin film magnetic head to be manufactured later.
Next, after forming, on the second magnetic layer 7, a write gap layer 8 made of a nonmagnetic material such as alumina to have a thickness of about 200 nm and a given pattern. After forming a magnetic layer made of a magnetic material having a high saturation magnetic flux density such as permalloy (Ni 50%: Fe 50%) and iron nitride (FeN), this magnetic layer is shaped into a given pattern by a highly precise mask alignment to form a pole chip 9. A width W of the pole chip 9 defines a track width. Therefore, in order to attain the high surface recording density, it is necessary to narrow the width W of the pole chip 9 as small as possible.
During the formation of the pole chip 9, a dummy pattern 9' for connecting the magnetic layer 11 for connecting the second magnetic layer constituting the bottom pole with a third magnetic layer constituting the top pole is formed. This dummy pattern makes the formation of a through hole easy after mechanical polishing or chemical-mechanical polishing (CMP).
Then, in order to prevent an increase of an effective track width, that is, in order to prevent a spread of a magnetic flux at the lower pole during a writing operation, the gap layer 8 and second magnetic layer 7 constituting the bottom pole in a vicinity of the pole chip 9 are removed by an ion beam etching such as an ion milling. This condition is shown in FIG. 5, and the thus formed structure is called a trim structure, and the trim structure constitutes a pole portion of the second magnetic layer.
Furthermore, as depicted in FIG. 6, an insulating layer 10 made of an alumina is formed to have a thickness of about 3 .mu.m, and then an assembly is flattened by CMP. Then, after forming an electrically insulating photoresist layer 11 in accordance with a given pattern by a highly precise mask alignment, a first layer thin film coil 12 made of, for instance a copper is formed on the insulating layer 11.
Next, as depicted in FIG. 7, after forming an insulating photoresist layer 13 on the first layer thin film coil 12 by a highly precise mask alignment, a surface of the photoresist layer is flattened by baking at a temperature of, for instance 250-300.degree. C.
A reason for forming the photoresist layers 11, 13 and 15 by a highly precise mask alignment is that the throat height TH and MR height are determined with respect to edges of these photo-resist layers on a side of the pole portion.
Next, as shown in FIG. 9, a third magnetic layer 16 made of, for instance a permalloy is formed selectively on the pole chip 9 and photoresist layers 11, 13 and 15 such that the third magnetic layer has a thickness of 3 .mu.m and is shaped into a desired pattern.
The third magnetic layer 16 is brought into contact with the first magnetic layer 7 at a position remote from the pole portion by means of the dummy pattern 9', and therefore the thin film coil 12, 14 pass through a closed magnetic path constituted by the second magnetic layer, pole chip and third magnetic layer.
Furthermore, an overcoat layer 17 made of an alumina is deposited on an exposed surface of the third magnetic layer 16.
Finally, a side wall at which the magnetoresistive layer 5 and gap layer 8 are formed is polished to form an air bearing surface (ABS) 18.
During the formation of the air bearing surface 18, the magnetoresistive layer 5 is also polished to obtain an MR reproducing element 19. In this manner, the above mentioned throat height TH and MR height MRH are determined by the polishing. This condition is shown in FIG. 10. In an actual manufacturing process, contact pads for establishing electrical connections to the thin film coils 12, 14 and MR reproducing element 19 are formed, but these contact pads are not shown in the drawings. FIG. 11 is a cross sectional view showing the pole portion of the thus manufactured combination type thin film magnetic head along a plane parallel with the air bearing surface 18.
As shown in FIG. 10, an angle .theta. between a straight line S connecting side edges of the photoresist layers 11, 13, 15 isolating the thin film coils 12, 14 and an upper surface of the third magnetic layer 16 is called an apex angle. This apex angle is one of important factors for determining a property of the thin film magnetic head together with the throat height TH and MR height MRH.
Furthermore, as shown in the plan view of FIG. 12, the width W of the pole chip 9 determines a width of tracks recorded on a record medium, and therefore it is necessary to make this width W as small as possible in order to realize a high surface recording density. The third magnetic layer 16 also has a narrow pole portion which is coupled with the pole chip 9, but its width is somewhat larger than the width of the pole chip 9. It should be noted that in the drawing, the thin film coils 12, 14 are denoted to be concentric for the sake of simplicity.
In the known method of manufacturing the thin film magnetic head, there is a special problem in the formation of the top pole after the formation of the thin film coil in a precise manner along the outwardly protruded coil portion, particularly along an inclined portion (Apex) thereof, said coil portion being covered with the photoresist insulating layers. That is to say, in the known method, upon forming the third magnetic layer, after a magnetic material such as permalloy is deposited by plating on the outwardly protruded coil portion having a height of about 7-10 .mu.m, a photoresist is applied to have a thickness of 3-4 .mu.m, and then the photoresist layer is shaped into a given pattern by utilizing the photolithography. Since a thickness of the photoresist layer provided on the upper portion of the coil portion should be at least 3 .mu.m, the photoresist layer has to be applied such that a portion of the photoresist at a bottom of the outwardly protruded coil portion would have a thickness of about 8-10 .mu.m.
On the other hand, in order to form a narrow track of the recording head near the edges of the photoresist insulating layers (for instance, layers 11 and 13 in FIG. 7), the top pole should be patterned to have a width of about 1 .mu.m. Therefore, it is necessary to form a pattern having a width of 1 .mu.m in the photoresist layer having a thickness of 8-10 .mu.m.
However, when such a narrow pattern having a width of 1 .mu.m is to be formed with the thick photoresist layer having a thickness of 8-10 .mu.m, a top pole which can realize a narrow track could hardly be manufactured accurately due to a deformation of a pattern by light reflection during a light exposure in a photolithography and an inevitable decrease in a resolution caused by a large thickness of the photoresist layer.
In order to mitigate such a problem, as shown in FIGS. 1-12, the top pole is divided into the pole chip 9 and the yoke portion (third magnetic layer 16) connected therewith, and the width W of the pole chip 9 is narrowed to decrease a width of the record track width.
However, the thin film magnetic head, particularly the recording magnetic head formed in the above mentioned manner still has the following problems.
If there is an alignment error in the photolithography for forming the third magnetic layer 16 on the pole chip 9 having the narrow width W, a center of the pole chip 9 and a center of the pole portion 20 of the third magnetic layer 16 viewed from the air bearing surface 18 might be shifted relative to each other. If the center of the pole chip 9 is deviated from the center of the pole portion 20 of the third magnetic layer 16, there might be produced a large leakage of the magnetic flux from the pole portion of the third magnetic layer and data might be written by this leaked magnetic flux. Therefore, an effective track width is increased and data might be recorded in a region other than a desired region into which the data has to be recorded.
The surface of the pole chip 9 is coupled with the surface of the third magnetic layer. In order to make the width W of the pole chip narrow as explained above and in order to attain a good magnetic property, a length of the pole chip has to be short such as about 1 .mu.m. Therefore, a contact area of the pole chip and third magnetic layer is small. Moreover, the third magnetic layer is brought into contact with the pole chip perpendicularly, and thus a magnetic flux is liable to be saturated at this portion, a writing property, particularly a magnetic flux rise time is degraded.
In the known thin film magnetic head, the edge of the pole chip 9 opposite to the air bearing surface 18 is used as a reference position of throat height zero. However, since the pole chip has the small width W, the edge of the pole chip is rounded off and therefore a position of the edge of the pole chip might be shifted. In the conventional combination type thin film magnetic head, although the throat height TH and MR height MRH have to be set accurately with reference to the throat height zero position, since the reference position of throat height zero might deviate during the manufacturing process and could not be defined accurately, the thin film magnetic head having desired throat height TH and MR height MRH according to the desired design values could not be manufacture with a high yield.
In the known thin film magnetic head so far explained, there is provided the pole chip 9, but it has been also known a thin film magnetic head having no pole chip. FIG. 13 is a cross sectional view showing such a thin film magnetic head while the overcoat layer is removed, and FIG. 14 is a cross sectional view depicting the pole portion. Furthermore, FIG. 15A shows a condition before forming the trim structure by using the third magnetic layer 16 constituting the top pole as a mask, and FIG. 15B is a plan view after the formation of the trim structure. In these drawings, portions similar to those shown in FIGS. 1-12 are denoted by the same reference numerals used in FIGS. 1-12.
As depicted in FIG. 15, a pole portion of the third magnetic layer 16 has a narrow width W, and since a width of a track on a magnetic record medium is defined by said width W, the width W should be as small as possible in order to realize a high surface recording density.
In this manner, also in the thin film magnetic head without the pole chip, the above mentioned problems equally occur in the miniaturization of the pole portion of the top pole. That is to say, in order to miniaturize the pole portion of the inductive type thin film magnetic head as well as to improve the magnetic characteristics, it is required to make the throat height HT and MR height MRH as small as possible, but in the conventional combination type thin film magnetic head, it is quite difficult to form the small throat height TH and MR height MRH to have designed values.
The throat height TH and MR height MRH have to be formed accurately with reference to the position of throat height zero, however in the known combination type thin film magnetic head, there is a problem that the reference position of throat height zero could not be set accurately. That is to say, the insulating layers 13, 15 covering the thin film coils 12, 14 are made of a photoresist, and the insulating layers are subject to the reflow at a temperature about 250.degree. C. in order to flatten the thin film coils and to isolate coil windings and the pattern and dimension of the insulating layers might fluctuate. As a result of this, the throat height TH and MR height which are formed with reference to the position of the edges of the insulating layers might deviate from design values. Particularly, when the photoresist constituting the insulating layers 13, 15 is thick, a deviation of the pattern might amount to a very large value such as about 0.5 .mu.m. Therefore, a fine throat height of order of sub-micron which is required for a high frequency thin film magnetic head could not be formed in a highly reproducible manner. Moreover, a variation in a thickness of the insulating layers 13, 15 also results in the deformation of the pattern, and a thin film magnetic head having desired throat height TH and MR height MRH could not be manufactured with a high yield.
In the known combination type thin film magnetic head, the polishing of the air bearing surface is carried out by monitoring a resistance value of the GMR reproducing element such that the polishing is continued until the resistance value becomes a given value, and a dimension of the throat height is not measured at all.
However, even if the MR height MRH has a desired value, the throat height TH could not have a desired value and many magnetic heads could not be manufactured correctly. Particularly, when the reference position of throat height zero deviates due the deformation of the pattern of the insulating layers 13, 15, the throat height TH is not formed to have a desired value, even if the MR height MRH is formed to have a desired value.
Moreover, also in the conventional thin film magnetic head illustrated in FIGS. 13-16, in order to make the effective track width substantially identical with a width of the pole portion of the third magnetic layer 16 constituting the top pole, the surface of the second magnetic layer 7 constituting the bottom pole is partially removed by performing the etching using the pole portion of the third magnetic layer 16 to form the trim structure. During this etching, i.e. ion beam etching, the insulating layers 13, 15 made of a photoresist are also etched and the edges of these insulating layers 13, 15 on the side of the air bearing surface are retarded by a distance of about 1.0-1.5 .mu.m. The edges of the insulating layers 13, 15 on the side of the air bearing surface define the above mentioned reference position of throat height zero, and this reference position of throat height zero fluctuates by the etching and the throat height could not be formed to have a desired design value. Particularly, in the high frequency thin film magnetic head having the short throat height TH not larger than 1 .mu.m, the fact that the position of the edges of the insulating layers 13, 15 on the side of the air bearing surface over a distance of about 1.0-1.5 .mu.m results in a very serious problem.
Furthermore, since the position of the edges of the insulating layers 13, 15 on the side of the air bearing surface are retarded during the etching for forming the trim structure, a part 20 of the insulating layer underneath the pole portion of the third magnetic layer 16 might be damaged as shown in FIG. 16 due to a handling shock during the wave process, and in an extreme case, a part of the insulating layers 13, 15 might be pealed-off. When a part of the insulating layers 13, 15 is pealed-off and a space is formed, oil and polishing liquid might penetrate into this space, and the third magnetic layer 16 might be etched and its property might be deteriorated.